1. Field of the Invention
The present invention relates to an oil-hydraulic circuit of a belt-type continuous variable speed-change transmission.
2. Description of the Related Art
A belt-type continuous variable speed-change transmission generally is so arranged as to stretch a belt over both a primary pulley connected to the input shaft and a secondary pulley connected to the outlet shaft. By increasing and decreasing oil pressure of the respective cylinders of those pulleys and by causing a relative change in the respective groove widths of such pulleys, the transmission causes a change in the speed. As a conventional control apparatus for use on this belt-type continuous variable speed-change transmission, there is, for example, the one that is disclosed in Japanese Patent No. 2848177.
However, in this conventional control apparatus for use on the belt-type continuous variable speed-change transmission, to provide for a simple case where the first or the second control valve is not functioning properly, the third control valve and the speed-change-limiting valve must be additionally provided. Therefore, there exists the problem that the cost of the product inconveniently rises due to an increase in the number of parts.
The present invention has been made in order to solve the above-described problems and has an object to provide an oil-hydraulic circuit of a belt-type continuous variable speed-change transmission, in which, when a failure occurs in the control circuit, the safety of travel of the vehicle is reliably ensured with a simple construction of the oil-hydraulic circuit to thereby enable the simplification of the oil-hydraulic circuit and the reduction in the cost.
To attain the above object, in the oil-hydraulic circuit of a belt-type continuous variable speed-change transmission according to the first aspect of the invention, there is provided a fail-safe element that, when having detected a failure of the first control element, second control element, or operation-controlling element, causes an increase in the oil-hydraulic operating fluid supplied to the secondary cylinder and simultaneously causes the operating oil pressure regulated by the pressure-regulating element to continue to be supplied to the primary cylinder.
Accordingly, even when the failure-detecting element has detected a failure, the supply of the operating oil pressure-regulated by the pressure-regulating element to the primary cylinder continues to be performed. Therefore, oil-hydraulic operating fluids that are the same high pressure are supplied to the secondary cylinder and to the primary cylinder. However, because the pressure-receiving area of the primary cylinder is made greater than that of the secondary cylinder, the change-of-speed ratio is made to be at a value equal to or smaller than 1. Therefore, even during high-speed travel, the engine is prevented from having too rapid revolution.
In the oil-hydraulic circuit of a belt-type continuous variable speed-change transmission according to the second aspect of the invention, oil-pressure-reducing means is disposed in the oil passage between the pressure-regulating element and the primary cylinder, the oil-pressure-reducing means reducing the oil pressure when this oil pressure within the oil passage has become equal to or higher than a prescribed value. Accordingly, the oil-hydraulic operating fluid pressure regulated by the pressure-regulating element and supplied to the secondary cylinder is ensured to be at the necessary minimum pressure level enabling the prevention of belt slippage. And accordingly, the loss of the driving power for the oil pump can be decreased. Accordingly, even at the time of a failure, it is possible to achieve reduction in the consumption of fuel.
In the oil-hydraulic circuit of a belt-type continuous variable speed-change transmission according to the third aspect of the invention, the oil-pressure-reducing means is disposed on the operating oil passage between the speed-change-ratio-controlling element and the primary cylinder. Accordingly, an unnecessary increase in the line pressure is prevented and, at the same time, the level of the oil-hydraulic operating fluid supplied to the primary cylinder is reliably prevented from becoming equal to or higher than that corresponding to a prescribed value.
In the oil-hydraulic circuit of a belt-type continuous variable speed-change transmission according to the fourth aspect of the invention, the oil-pressure-reducing means includes a first outlet valve disposed in an operating oil passage between the pressure-regulating element and the speed-change-ratio-controlling element and a second outlet valve disposed between the speed-change-ratio-controlling element and the primary cylinder, wherein the outlet pressure of the first outlet valve is set to be at a level higher than that of the second outlet valve. Accordingly, in the case where even though the first control element, second control element, and operation-controlling element are operating normally, line pressure equal to or higher than the set outlet pressure of the first outlet valve occurs in the operating oil passage between the pressure-regulating element and the speed-change-ratio-controlling element due to the sticking of the pressure-regulating element""s moving elements, etc., it becomes possible to reduce the resulting oil pressure through the operation of the first outlet valve. On the other hand, even when the first control element, second control element, or operation-controlling element malfunctions with the result that the line pressure has become high in level, the oil-hydraulic operating fluid that is supplied at that time is decreased through the second outlet valve. Therefore, an unnecessary increase in the line pressure is prevented.
In the oil-hydraulic circuit of a belt-type continuous variable speed-change transmission according to the fifth aspect of the invention, the outlet passage of the oil-pressure-reducing means is connected to a lubrication passage. Accordingly, at the time of a failure, the pressure of oil-hydraulic operating fluid supplied to the secondary cylinder is increased, and the outlet of operating fluid from the pressure-regulating element is decreased, thereby possibly causing deficiency in lubrication. However, because the operating oil going from the oil-pressure-reducing means is supplemented to the lubrication passage via the outlet passage, it is possible to prevent the movement seizure of the portions where lubrication is necessary.
In the oil-hydraulic circuit of a belt-type continuous variable speed-change transmission according to the sixth aspect of the invention, the fail-safe element controls the pressure-regulating element so as to cause an increase in the oil-hydraulic operating fluid supplied to the secondary cylinder and controls the speed-change-ratio-controlling valve so as to cause the operating oil pressure regulated by the pressure-regulating element to continue to be supplied to the primary cylinder. Accordingly, by controlling the pressure-regulating element and speed-change-ratio-controlling element, the oil-hydraulic operating fluid supplied to the secondary cylinder is reliably increased while the operating oil that is pressure-regulated by the pressure-regulating element continues to be supplied to the primary cylinder.
In the oil-hydraulic circuit of a belt-type continuous variable speed-change transmission according to the seventh aspect of the invention, the pressure-regulating element is constructed so that, as the first control element operates less, the oil-hydraulic operating fluid supplied to the secondary cylinder increases, the speed-change-ratio-controlling valve is constructed so that, as the second control element operates less, the oil-hydraulic operating fluid pressure-regulated by the pressure-regulating element is supplied to the primary cylinder in greater amounts, and, when the failure-detecting element has detected a failure, the fail-safe element causes a reduction in the amount of operation of the first control element and that of the second control element. Accordingly, with the use of such a simple construction as to decrease the amount of operation of the first and the second control element, the oil-hydraulic operating fluid supplied to the secondary cylinder is reliably increased while the operating oil pressure-regulated by the pressure-regulating element can continue to be supplied to the primary cylinder.
In the oil-hydraulic circuit of a belt-type continuous variable speed-change transmission according to the eighth aspect of the invention, the first control element is constructed with a first electromagnetic valve that discharges a control pressure according to the electricity supplied from the operation-controlling element, the second control element is constructed with a second electromagnetic valve that discharges the control pressure according to the electricity supplied from the operation-controlling element, the pressure-regulating element is constructed with a pressure-regulating valve, the speed-change-ratio-controlling valve is constructed with a speed-change-ratio-controlling valve, whereby the control pressure discharged from the first electromagnetic valve is led to one side of the pressure-regulating valve via a first operating-oil passage, with the result that the pressure-regulating valve is controlled according to the control pressure from the first electromagnetic valve while the control pressure discharged from the second electromagnetic valve is led to one side of the speed-change-ratio-controlling valve via a second operating-oil passage, with the result that the speed-change-ratio-controlling valve is controlled according to the control pressure from the second electromagnetic valve, and the fail-safe element includes a first urging-force generating element that is disposed on the other side of the pressure-regulating valve and that generates an urging force resisting the control pressure of the first electromagnetic valve which, as the control pressure from the first electromagnetic valve decreases, increases the oil-hydraulic operating fluid supplied by the pressure-regulating valve to the secondary cylinder, and a second urging-force generating element that is disposed on the other side of the speed-change-ratio-controlling valve and that generates an urging force resisting the control pressure of the second electromagnetic valve which, as the control pressure from the second electromagnetic valve decreases, increases the supply to the primary cylinder of the operating oil pressure-regulated by the pressure-regulating valve. Accordingly, when a failure occurs, the first urging-force generating element causes the pressure-regulating valve to operate so that the oil-hydraulic operating fluid supplied to the secondary cylinder is increased, while the second urging-force generating element causes the speed-change-ratio-controlling valve to operate so that the operating oil pressure-regulated by the pressure-regulating element and supplied to the primary cylinder may continue to be supplied thereto. As a result of this, it is possible to simplify the oil-hydraulic circuit and reduce the cost without separately providing a special control valve for fail-safe operation.